The present invention concerns a trailer coupling device, including a first part, which is adapted to be attachable to a towing vehicle, and a second part, which is adapted to be coupled to a trailed vehicle and to be releasably attachable to the first part, the first part including an opening, in which the second part is introduceable, and a locking bolt, which is displaceable in its axial direction into the opening in the first part to lock the second part in the position thereof where it is introduced in the opening by engagement in a locking recess therein, and which is urged by a spring in the direction towards the opening in the first part and manually operable in the opposite direction.
A device of this kind is known from SE-B-8400369-8 and serves on one hand to enable the use of interchangeable second parts, such as various towing devices of the ball type or various cargo carrying devices, such as bicycle carriers, and on the other hand to lock the second part against being pulled out and/or being rotated in the position thereof where it is introduced in the first part. In the known device, the spring constantly acts against the locking bolt to keep it in its locking, advanced position, in which further movement of the locking bolt is prevented by an abutment in the housing, in which it is guided. Retraction of the locking bolt --in order to release the second part for substitution or rotation thereof --is carried out manually against the action of the spring. The locking bolt comprises two parts threaded in each other, viz. a foremost, non-rotatable part and a rear, rotatable part, which are screwed from each other in order to prevent inadvertent release of the second part, so that the rear one of these parts abuts a portion of the housing, in which the locking bolt is guided. In this position the locking bolt is positively prevented from backward movement, i.e. to release the second part. Simultaneously, the locking bolt is merely forced harder against the abutment in the guide housing, i.e., it is also prevented form further forward movement into the locking recess. Thus, there is no possibility to achieve compensation for e.g. wear caused by play between the locking bolt and the locking recess in the second part, or, more generally, between the first part and the second part, since the locking bolt cannot be positively displaced beyond the abutment in the guide housing in order to --as a complement to the spring force --be further forced into the locking recess.